The quality and shelf life of fresh produce is enhanced by enclosing them in packaging that modifies or controls the atmosphere surrounding the product. The technology is referred to as MAP (modified atmosphere packaging) or CAP (controlled atmosphere packaging). MAP/CAP provides increased quality and longer shelf life resulting in fresher products for the consumer, less waste from spoiled produce, better inventory control, and appreciable overall savings for the food industry at both the retail and wholesale levels.
CAP of fresh produce is just a more controlled version of MAP. It involves a precise matching of packaging material gas transmission rates with the respiration rates of the produce. The goal in fresh produce packaging is to use MAP/CAP to preserve produce quality by reducing the aerobic respiration rate but avoiding anaerobic processes that lead to adverse changes in texture, flavor, and aroma, as well as an increased public health concern. For each respiring produce item, there is an optimum O2 and CO2 level that will reduce its respiration rate and thereby, slow aging and degradation processes. Different fresh produce items have different respiration rates and different optimum atmospheres for extending quality and shelf life.
Bananas pose a unique challenge in MAP/CAP. There is a complex system for distributing bananas which involves harvesting the fruit when it is green, packing the green fruit in cartons, shipping the fruit to distant markets via ocean liners, initiating ripening at the receiving port by gassing the green fruit with ethylene, and after sufficient time is allowed for ripening, the fruit is shipped to the wholesale or retail markets.
Unlike bananas, plantains are sold both as unripe fruit, as well as ripened yellow fruit in the supermarket. Providing ripened fruit to the wholesale or retail markets pose similar challenge as with bananas.
More bananas are consumed around the world than any other fruit. According to FAO, worldwide banana exports are valued at over $4.7 billion per year. Large volumes of bananas are grown and harvested in South America, packed in 40 lb boxes with liners and shipped to ports in the U.S., Europe, and Asia where they are gassed with ethylene to initiate the ripening process. Costa Rica and Ecuador are the two largest exporters of bananas.
Plantains are not as widely consumed fruit as bananas, but it has established steady markets especially in the United States. Most of the plantains exported to the United States are shipped in 50 lb boxes from South America.
In order to provide the consumers the best quality of bananas and plantains, the producers are constantly trying to find a technology that would provide maintenance of the green life of bananas during shipping and on the other hand uniform ripening and long yellow life. Banana or plantain green life and banana or plantain shelf life are two competing physiological conditions. By drastically decreasing the oxygen content green life is greatly increased. On the other hand ripening requires ethylene gas.
The currently available technology to maintain the green life while shipping includes depriving oxygen from the bananas or plantains. This may take place, for example, by closing the bananas or plantains in plastic bags having low permeability to oxygen.
Several types of plastic bags have been tested with bananas in an attempt to control ripening and quality. Banavac bags are 1.0-1.5 mil polyethylene bags without holes and are used when green life extension is needed and on vessels that do not have controlled atmosphere. Banavac bags must be torn open before the ripening cycle (ethylene gas treatment) can be initiated, because the gas does not penetrate the bag. The need to rip open the bags before gassing results in added labor costs. Some Banavac bags have ripcords to make it easier to tear open the bags, but easy tear bags do not maintain adequate modified atmospheres because they leak.
Polypack bags are 0.7 mil polyethylene (PE) bags with holes punched in the bags. This bag is used in European markets under most conditions. These bags can not be used to delay ripening of the fruit or to extend the shelf life of bananas because there is no control of the atmosphere inside this type of bag. Similarly, Tubopak bags have holes punched in the bag so that no atmosphere control can be obtained.
Patent application publications WO 01/92118 A2, WO 03/043447 A1, and EP 1 516 827 A1 describe banana packaging consisting of a polymer-coated microporous membrane applied over specifically sized holes in the container. The breathable membrane controls the oxygen, carbon dioxide, and ethylene contents inside the package to control ripening (without opening the bag) and to extend the shelf life of bananas after ripening. The breathable patch is generally produced by normal plastic extrusion and orientation processes. By way of example, a highly filled, molten plastic is extruded onto a chill roll and oriented in the machine direction using a series of rollers that decrease the thickness of the web. During orientation, micropores are created in the film at the site of the filler particles. Next, the microporous film is converted into pressure sensitive adhesive patches or heat-seal coated patches using narrow web printing presses that apply a pattern of adhesive over the microporous web and die-cut the film into individual patches on a roll. These processes typically make the cost of each patch too expensive for the wide spread use of this technology in the marketplace, particularly for cost-sensitive produce items like bananas or plantains.
In addition, the banana or plantain packer has to apply the adhesive-coated breathable patch over a hole made in the primary packaging material (bag) during the packaging operation. To do this, the packer must purchase hole-punching and label application equipment to install on each packaging equipment line. These extra steps not only increase packaging equipment costs, but also greatly reduce packaging speeds, increase packaging material waste, and therefore, increase total packaging costs.
Microporous material can be used only as patches on the packages basically due to two reasons: 1) high cost of the material and 2) the material is inherently opaque thereby allowing inspection of the packed material only when applied as patches. Specifically related to banana or plantain packaging, the microporous material has to be attached only to a limited area in order to be able to control the atmosphere inside the bag. If the bag would be made fully out of the microporous material the total OTR of the bag would be much too high, resulting in ambient air conditions (20.9% O2/0.03% CO2) inside the bag. This would prevent the controlled ripening of the bananas or plantains and yellow life extension.
An alternative to microporous patches for MAP/CAP of bananas or plantains is to microperforate polymeric packaging materials. Various methods can be used to microperforate packaging materials: cold or hot needle mechanical punches, electric spark and lasers. Mechanical punches are slow and often produce numerous large perforations (1 mm or larger) throughout the surface area of the packaging material, making it unlikely that the atmosphere inside the package will be modified below ambient air conditions (20.9% O2, 0.03% CO2). Equipment for spark perforation of packaging materials is not practical for most plastic converting operations, because the packaging material is typically submerged in either an oil bath or a water bath while the electrical pulses are generated to microperforate the material.
The most efficient and practical method for making microperforated packaging materials for controlled atmosphere packaging of fresh produce is using lasers. U.S. Pat. No. 5,832,699, UK Patent Application 2 221 692 A, and European Patent Application 0 351 116 describe a method of packaging plant material using perforated polymer films having 10 to 1000 perforations per m2 (1550 per in2) with mean diameters of 40 to 60 microns but not greater than 100 microns. The references recommend the use of lasers for creating the perforations, but do not describe the equipment or processes necessary to accomplish this task. They describe the limits of the gas transmission rates of the perforated film: OTR (oxygen transmission rate) no greater than 200,000 cc/m2-day-atm (12,903 cc O2/100 in2-day-atm), and MVTR (moisture vapor transmission rate) no greater than 800 g/m2-day-atm (51.6 g/100 in2-day-atm). However, the OTR of a film does not define the total O2 Flux (cc O2/day-atm) needed by a fresh produce package to maintain a desired O2 and CO2 internal atmosphere based on the respiration rate of the specific produce item, the weight of the produce enclosed in the package, the surface area of the package, and the storage temperature. A 50-micron perforation has a very small surface area (1.96×10−9 m2) and a low O2 Flux (about 80 cc/day-atm) compared to its very high OTR (>200,000 cc O2/m2-day-atm). Therefore, one 50-micron perforation would exceed the OTR limit of this invention. Furthermore, since the microperforations placed throughout the length and width of the packaging and are not registered in a well-defined area on the packaging, they can be easily occluded during pack out, shipment or display by produce, adjacent bags, or marketing labels applied on the package. The result is a wide variability in the gas transmission rates of the packaging materials.
U.S. Pat. Nos. 6,441,340, 6,730,874, and 7,083,837 disclose a microperforated packaging material, where the microperforations are specifically tailored in size, location and number for the specific produce to maintain pre-selected O2 and CO2 concentrations. The method to make registered microperforations according to these patents uses a CO2 laser and a sensor mechanism.
Microperforated packaging material can be used successfully to control the O2 and CO2 concentrations inside fresh produce packaging. However, the fact that the microperforations are through holes or drill holes through the material would suggest that the material is not at all functional for banana packaging. This is for two reasons: one would expect that the holes would provide an easy access for microorganisms into the package and secondly, one would expect that the material would not effectively prevent dehydration of the bananas. It also seems that the packing into bags according to this disclosure have a twofold effect on disease development: Infections that have occurred after cutting (in the field) and during the washing/packing operations are unable to develop further due to direct action of high CO2 inhibiting fungal growth, and indirect effect of high H2O reduces the severity of symptoms.
The concern of the access of microorganisms into the banana or plantain package is a real one, as one of the main problems with banana and plantain shipping is infection of the fruit by crown rot disease. Crown rot is a pathological disease caused by a fungal complex (species of Fusarium, Penicillium and Colletotrichum) and, although infection occurs during harvesting and packing, symptoms may not be obviously until after ripening.
Accordingly, currently available technologies provide materials for generally packaging fresh fruits. Moreover, currently available technologies provide materials to specifically pack bananas for shipping. Even if microporous membranes are capable of controlling the ripening of bananas or plantains, there is a clear need for a cheaper technology. Other currently available banana or plantain packaging technologies leave such unresolved problems as uneven ripening, and exposure of the bananas or plantains to post harvest diseases during shipping.
What is needed to address the shortcomings in current banana/plantain packaging is an efficient and less costly system to produce MAP/CAP packaging for bananas and plantains. There is a clear need for a system that would allow for transmission of oxygen, carbon dioxide, and ethylene gases into and out of the packaging for optimum quality preservation of the bananas or plantains in terms of green life, ripening rate, and extended shelf life. Moreover, there is a need for a system ensuring uniformity of banana and plantain quality with regard to ripening and shelf life. Even further there is a clear need for a system that would prevent post harvest diseases and retain the fresh weight of the bananas and plantains during transport and storage.